The present invention relates generally to the art of processing web-like material, and more specifically to a method and apparatus for automatically changing a plurality of cores while winding a series of web segments onto the cores.
Web processing lines, whether for forming, printing, laminating or otherwise processing the web, frequently have as a final station a winding machine for winding the web onto one or more cylindrical cores. As each core fills with material and becomes a large roll, the winding operation must be terminated on that core and started on a new core. The core changing operation is often done automatically, without slowing down or stopping travel of the web through the line. Such "on the fly" changeover offers several advantages: first, downtime during the core changeover is avoided, increasing the overall efficiency of the web processing line; second, and often more important, other operations on the line upstream from the winder need not be shut down during core change. This is especially important in certain web forming operations such as the manufacture of a blown film web, where process parameters must be carefully adjusted during start-up, and an interruption in the process requires a long, involved procedure in order to resume the formation of the web.
In addition to winding the web on a roll, it is often desirable to slit the web longitudinally, and to wind the resulting web segments on shorter, individual cores. Machines performing this function are called slitter/rewinders. Such an operation is often performed off-line by a machine that unwinds a web from a "master" or "jumbo" roll produced on a web forming line, slits the web into a series of segments and rewinds the segments onto smaller cores. The operation is performed off-line because slitter/rewinders often require the web to be stopped or slowed down during core changing.
As a web of material is wound on a roll (hereinafter called a "winding roll"), there is a tendency for air to become entrapped between the web and the roll as the web wraps onto the roll. To overcome this problem, lay-on rolls are often used in winding operations. Lay-on rolls are free-wheeling rolls that apply pressure to the outermost layer immediately after it is wound onto the rolls. They are used to prevent air from being pulled into the rolls between adjacent layers. In such an arrangement, the torque required to maintain tension on the web as it is wound onto the roll is provided by driving the core at the center of the roll, a technique called "center winding." Because the diameter of the roll changes as the process progresses, the torque and speed at which the core is driven must change as the roll increases in diameter in order to maintain constant web tension. Even with such controls, however, such an operation may result in "cinching" of the roll and an unevenness in the tightness of the roll between the inner layers and the outer layers.
Lay-on rolls may be adapted to maintain continuous contact with a winding roll during an automatic core changeover. For example, U.S. Pat. No. 4,529,141 discloses a rewinding machine having a turret on which winding cores are supported at diametrically opposite positions. During winding of a web onto a core, a primary frame-mounted lay-on roll applies pressure to the outside of the winding roll, reducing the amount of air entrapped between the layers. Before changing cores, an auxiliary lay-on roll, which is mounted on the turret, is indexed into contact with the web in order to continue to provide pressure on the outside surface of the web during the indexing of the turret. The primary lay-on roll is then retracted, the turret is rotated 180.degree. and the web is severed and attached to an empty core in the opposite position on the turret. Lay-on rolls such as those disclosed in the '141 patent are not driven, and therefore play no part in maintaining tension on the web, which is done by driving the winding roll itself. Because changeover is automatic between cores, this machine may be used at the end of a line without the necessity of stopping or slowing down the line in order to change cores. The machine, however, is not capable of slitting the web into separate segments, and this operation, if required, must be done later off line. Furthermore, because the winding rolls are driven from the core, cinching and uneven tension in the winding roll may be a problem.
A "surface winding drum" is used in order to reduce the cinching and unevenness problems associated with driving the winding operation from the center of the winding roll. A surface winding drum is driven at the surface speed of the incoming web, and is urged against the winding roll at a predetermined pressure at the point where the web joins the winding roll. The web typically travels some angular distance around the winding drum before being transferred to the winding roll at the nip between the two. By driving the surface winding drum at the web surface speed, the surface speed of the outer layer of the winding roll is controlled without transferring torque through the layers of the winding roll. The winding roll may also be driven from the core at a controlled torque in order to prevent loosening of the inner wraps and unevenness that might otherwise result from friction of the core chuck bearings and the angular momentum of the roll during the gradual deceleration of angular velocity during winding.
An example of a surface winding drum is disclosed in U.S. Pat. No. 3,157,371. A single surface winding drum is used in conjunction with two winding rolls contacting diametrically opposite points on the winding drum. The winding rolls are mounted on respective turrets that urge the winding rolls against the winding drum. The incoming web of material is slit by a knife, and the resulting two segments are wound onto the two rolls. In order to change a core, auxiliary lay-on rolls mounted on the turrets are indexed into contact with the completed winding rolls, and the turrets are rotated, indexing new cores into position proximate the winding drum. The web is then severed and attached to the new cores. During rotation of the turrets, the winding drum is not in contact with the active winding rolls. During that time, the winding rolls are instead driven from their centers. Thus, cinching or uneven winding may occur during core changing as torque is transmitted through the roll.
Another winding drum arrangement having automatic core changing is disclosed in U.S. Pat. No. 4,541,583. In this arrangement, primary and secondary surface winding drums are mounted on arms rotatably mounted to the frame, and cores and winding rolls are mounted on a turret. In order to change cores, the secondary winding drum is brought into contact with an empty core, trapping the web between, and a knife and brush assembly is simultaneously indexed across the web, cutting it and attaching it to the core. The newly active core is then indexed to the primary winding position on the turret, and the primary surface winding drum is brought into contact with the active winding roll before contact is broken with the secondary winding drum. Thus, contact is maintained between a winding drum and the winding roll at all times during winding. Such a design does not lend itself to slitting because there is no provision for applying uniform winding pressures for individual rolls created by individual segments of the slit web. Such provisions are necessary, for example, if the unslit web has micrometer thickness variations across its width. In the above-described machine, a single winding roll to winding drum distance is maintained across the width of the web, regardless of thickness variations. Thus, the winding machine disclosed in the '583 patent is not easily adaptable for slitting. If slitting is required for a web processed on such a machine, it must be done by a slitter/rewinder in a subsequent off-line operation.
When a web is slit into individual segments, the center-to-center distance between the winding rolls and the surface winding drum must be adjusted individually for the individual winding rolls. As noted, the winding pressure would otherwise vary on individual winding rolls depending on the web thickness for that individual roll. One way of providing individual winding pressure for each web segment is mounting the individual winding rolls on winding arms. Such a system is disclosed in U.S. Pat. No. 4,697,755. The winding arms permit a force-based adjustment of the relative positions of the winding roll and the surface winding drum for each individual winding roll, while using a single, continuous surface winding drum to wind a plurality of winding rolls. Furthermore, the winding arms may be adjusted during a changeover to accommodate varying segment widths in a slitting/rewinding operation. Each of two surface winding drums in the '755 patent is associated with a series of winding arms, pairs of which support winding rolls receiving alternating web segments. Thus, adjacent web segments are routed to different surface winding drums, providing clearance between the segments for chucks and for the winding arms. No provision is provided for automatic core changing in the slitter/rewinder disclosed in the '755 patent. Instead, the winding operation must be stopped and the arms moved to a load/unload position remote from the surface winding drums, where completed winding rolls are removed and replaced with empty cores.
There therefore remains a need for a machine capable of slitting a relatively wide web into a plurality of segments and winding the segments onto separate cores, wherein the segments are wound relatively evenly throughout the roll, are wound without applying undue torque through the layers of the web, and are wound with substantially the same winding pressure applied to each of the rolls; while at the same time, providing for automatic changeover of the cores without stopping the incoming web. Currently, where a web is formed in a process that cannot be stopped or slowed down, the web is either wound as a single, wide roll that is later slit and rewound, or the web is slit and wound on center winding machines not capable of eliminating the adverse effects caused by applying torque to the winding roll through the core.